In recent years, an organic light-emitting device provided with a plurality of organic light-emitting elements (organic EL elements) which are self-luminous type display elements has been attracting attention as a flat panel display.
An organic light-emitting element has such a structure that an organic light-emitting layer (organic compound layer) is interposed between two electrodes, and a transparent electrode made of, for example, indium tin oxide (ITO) is used for one of the electrodes in order that light emitted from the organic light-emitting layer may be extracted to the outside of a panel of the organic light-emitting device. The organic light-emitting element is typically formed on a substrate made of, for example, glass.
Further, the outer peripheral surface of the organic light-emitting element is sealed with a sealing material, and the element emits light as a result of the application of a voltage by an external driver circuit.
Since an organic light-emitting element is a self-luminous type display element, the element does not require any backlight, can be reduced in thickness, and has good visibility and a wide color reproduction range. In view of the foregoing, a plurality of corporations has been conducting research and development of organic light-emitting elements with a view to commercializing the elements.
At present, an organic light-emitting element has been already put into practical use as a display element for displays such as of an on-vehicle component and a mobile phone.
By the way, an organic light-emitting element which has the above characteristics is known to be extremely vulnerable to moisture in general.
For example, when moisture infiltrates into an organic light-emitting element, a non-light-emitting region referred to as a dark spot is generated, with the result that a problem concerning the lifetime of the element such as inability to maintain a light-emitting state occurs.
The following proposal has been conventionally made as a measure to solve the problem of the lifetime.
Flat glass is used as a sealing member for an organic light-emitting element substrate on which the organic light-emitting element is mounted, and a space between the organic light-emitting element substrate and the flat glass is filled with an inert gas. After that, the organic light-emitting element substrate is sealed with the flat glass by bonding the organic light-emitting element substrate and the flat glass with a UV curing resin of cation curing type (see Japanese Patent No. 3288242).
Another approach involving sealing the organic light-emitting element with a stacked structure having a barrier property has also been known (see Japanese Patent Application Laid-Open No. 2002-134271).
However, even when the organic light-emitting element substrate is sealed with the flat glass as a sealing member by using a UV curable adhesive of cation curing type as described in Japanese Patent No. 3288242, the infiltration of moisture from the resin portion as the adhesive or the infiltration of moisture from an interface at which the element is sealed with the flat glass cannot be completely prevented. As a result, considering the operating time of the element in practical use, the following problem exists: a dark spot is gradually generated, or a dark spot region gradually expands so that the element does not emit light.
Another approach involving interposing a moisture adsorbing member described in Japanese Patent No. 3288242 in order to adsorb moisture infiltrating into an organic light-emitting device in the above sealed structure is also known. However, when a sheet-shaped moisture adsorbing member is used, it is difficult to select flat glass as a sealing member because the sheet-shaped moisture adsorbing member has a thickness of, for example, about 250 μm.
Meanwhile, it is possible to adopt the so-called cap type glass which is dug down except the region where the organic light-emitting element substrate and flat glass are bonded to each other in order that a moisture absorbing member may be interposed, or a structure in which a spacer is provided between the organic light-emitting element substrate and the flat glass. However, such structures lead to cost increase or larger thickness of an organic light-emitting device.
The use of a stacked structure having barrier property is also considered as described in Japanese Patent Application Laid-Open No. 2002-134271 as another sealing approach. In the approach, since a moisture barrier film is directly formed on an organic light-emitting element, the barrier film may have a defect owing to, for example, an influence of a contaminant (an impurity or foreign matter) or a pinhole. In that case, moisture infiltrates into the organic light-emitting element through the defect to inhibit the light emission of the organic light-emitting element, with the result that the element becomes a non-light-emitting element. Further, moisture propagates from the non-light-emitting element into an organic light-emitting element adjacent to the non-light-emitting element to turn the adjacent organic light-emitting elements into non-light-emitting elements one after another. As a result, a wide range of an organic light-emitting device deteriorates, and hence the yield of the device is remarkably reduced. The inventor of the present invention has discovered that layers which mainly propagate moisture in this case are an element isolation layer formed between two adjacent organic light-emitting elements, an organic compound layer forming an organic light-emitting element, or a planarizing layer for covering an upper portion of a thin-film transistor (TFT) to planarize the covered surface thereof.